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MG MGB Technical - Current Draw questions

I am trouble shooting my girlfriend's dad's car and I have two very simple questions.
1. What is the current draw when the key is removed.
2. What is the current draw with the key in the ignition, but all accesories off?
John Doe

John - Is this a trick question? The way you have it worded, the answer is 0 in both cases, because you have never said that the ignition is turned on. If you have the key in the ignition and turned on, with all ancilleries off, the current flow would be whatever is being drawn by the coil, probably just a couple of amps (I don't have an exact figure). With the ignition off, current draw should be 0 unless there is a radio with a keep alive circuit (about 10 milliamps), a clock (about the same) and possibly up to 25 milliamps through the alternator's built in regulator (if it is a later model car).
Hope this helps - Dave
David DuBois

John Doe?

An MGB coil (or coil plus ballast) is about 3 ohms, giving about 4 amps (if the points are closed) with the ignition on, plus a few tens of milliamps for the tach and other electric instruments, ignition warning light and alternator regulator, plus an occasional pulse of the electric fuel pump. Plus any permanently powered items like the clock and radio mentioned, or alarm. Electronic ignition may draw *additional* current to the coil, or a much smaller current *in place* of the coil current, depending on type.

With the ignition off items like clock, alarm and some radios will still draw some current in the low tens of milliamps. An alternator will also draw some current but it is in the order of microamps.
Paul Hunt

What year is the car. 77 and later have a clock that has a small draw all the time.
Robert Novak

and the coil will draw zero amps if the points are open!
Chris at Octarine Services

This thread was discussed between 09/02/2004 and 10/02/2004

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